Household portable electronics, cellular phones and personal digital assistants, MP3 players, digital cameras and many other portable electronic devices are common consumer products. One attribute these consumer electronics share is the need to power and charge the batteries within the devices. Typically, each device is designed and built with its own unique power cell and charging adaptor or device. The charging adaptors typically run on electricity from an electrical outlet, a car cigarette lighter or from another suitable power supply wired to the device using a connector. Memory devices have a propriety connector. These methods of power transfer can be efficient, however, they also pose many problems.
First, current power transfer systems require a person to own and organize many rechargers or adaptors. Typically, both the power cells and the geometry of the device charging connectors are different depending on the size of the device, the charging voltage and the manufacturer of the device. The various chargers required to charge a collection of devices take up a lot of physical space and it can be difficult to remember which charger goes with which device.
Present solutions to charging consumer electronic devices can be messy, inconvenient and potentially dangerous. Consumer electronics chargers are typically plugged into common 120 or 240 volt wall sockets. It is often times desirable to charge several in one place to localize the mess of tangled cords and to provide convenience in locating a particular device. However, doing forces a user to use unsightly and potentially dangerous power strips and also to untangle and manage the various cords.
Another problem exists when trying to charge electrical devices where there is potential for water to come into contact with the device. Water corrodes metal coupling fixtures and can create electrical shorts. Electronics in the bathroom, such as electrical shavers and toothbrushes are especially prone to shorts. Likewise, charging devices near a pool, in a kitchen, outside or near another source of water can potentially ruin the device, or injure a user if the device or the charger gets wet and damaged.
Some inductive charging devices exist, but require the user to position the target device in some particular orientation on a charger which is burdensome and time consuming. Others waste a large amount of power to open space or are not powerful enough to conveniently charge modern devices.
Past attempts to use inductance to transfer power without requiring the precise orientation of the transducer and receiver has been proposed, but such attempts are so inefficient as to be not feasible. The principle drawback to such proposed charging systems is the amount of emitted ElectroMagnetic Interference (EMI) which is radiated into free space from such devices. To charge a remote device via remote inductive coupling requires a powerful signal to create adequate current flow in the target receiver. Such a signal is usually transmitted at one frequency, causing a strong spectral density of energy at that frequency and a large amount of radiated EMI. In reality, a monotonal signal cannot easily be produced, and typically a signal is formed with a distribution of frequencies, and harmonies centered upon the desired frequency. Therefore, EMI radiation from a powerful signal will interfere with the chosen frequency and a number of frequencies in close proximity to the radiated frequency.
ElectroMagnetic Interference (EMI) interrupts, obstruct, or otherwise degrades the performance of other circuitry. For example, EMI radiation can manifest itself as visual disturbances in visual devices such as televisions or computer monitors, or as audio disturbances in auditory devices such as radios. EMI radiation of particular frequencies are able to interrupt other signals, causing them to fail. For instance, interference around the 2.40 Ghz band is able to cause typical IEEE 802.11 Wi-Fi applications to fail. Furthermore, evidence exists that suggests that EMI can be harmful to human health.